Thanks for those updates, etc. re my query concerning the Blyth dredgers. I will look into them a lot closer tomorrow - damned laptop is playing up, and I am now using an XP laptop to keep up with things.
I used to go digging for ragworm and lug worm west of the West Staithes, i.e. down from where the old hospital and alkali works were. On an old map that area was shown as a ship 'turning basin'. At certain times of the year, when very low tides were experienced, I reckon I was 200-300 yds off those staithes, wearing wellies of course.

The top of what I was digging was pitch black, but 6-9 inches down it then became yellowish-sandy colour.